Interview on the Chicken or Egg problem of planet formation on Forbes! www.forbes.com/sites/bruced...

There is now a planetesimal bearing my name!! Nice to meet you 6054 P-L! And thank you IAU for making it happen. www.astronomie.nl/nieuws/17-ni...

Today was supposed to be a strike in the Netherlands on behalf of the higher education, against the major budget cuts. I think it got mostly cancelled due to the (completely coincidental) national train strike, but I was still wondering: is a strike the best way to protest as academics?

📣 Calling all rocky enthusiasts! We are thrilled to announce that the ROCKY WORLDS 4 Conference will take place 19-23 Jan 2026 in Groningen, NL 🇳🇱 This is the 4th Meeting in our series & we can't wait to see you there! Abstract submission is NOW OPEN groningen2026.rockyworlds.org/groningen-2026 🪐☄️🔭

Reviewing a proposal that cites one of my four 2021 papers. I checked the reference to see which one it is and the volume and page do not correspond to any of my papers. I asked ChatGPT and it claims is van der Marel & Mulders 2021 with a different volume and page. Did I reverse-engineer ChatGPT?

Tomorrow I will be at a 'talk show' on the great outdoors organized by TU Delft, talking about stories from observing nights at high altitude.

Winner of two prizes at the Leiden Allegro ARC node competition, both the one for most requested hours (of all proposals combined) and for the smallest proposal 😁 #almacycle12

The usual curve of proposal submissions on ALMA deadline day. It looks like we may end up a bit lower than last Cycle, unless we get a final sprint. I'm going to bet on 1560. What's your guess? #almacycle12

Looks like we are somewhat below the trend of last year. How many people are still submitting in the final 10 hours? #almacycle12

It is that time of the year again: #almacycle12

Really happy that three of my master students have managed to get a PhD position this year! Curious to see where their research is going to bring them 💪

here's my story on the (largely dutch) discovery that most protoplanetary disks are small and may spawn super-earths (for the website of sky and telescope): 🔭 skyandtelescope.org/astronomy-ne...

Exactly! Always consider the biases in your sample.

To accompany the press release from this morning on the compact disks, I made a short 2 minute video that showcases the key result. Enjoy watching! youtu.be/jvT1wD7yCec

Protoplanetaire schijven zijn veel kleiner dan eerder gedacht. Door Universiteit Leiden geleid onderzoek van Osmar M. Guerra-Alvarado et al., geaccepteerd voor publicatie in A&A. www.astronomie.nl/ni...

Super proud of my PhD student Osmar who discovered that the so-called 'compact disks' around young stars are REALLY REALLY small! Look at the full sample of Lupus disks, observed at 30 mas resolution with ALMA.

Help! The arxiv submission e-mail suddenly states that it may take 2 business days to go through technical/moderation checks. I thought this was always just 1 day. How long did it take you to get accepted on arxiv recently? I'm freaking out because this has to coincide with a press release tomorrow.

Le Monde reporting that a French scientist traveling to Houston to attend a conference was denied entry to US after a search of his phone & computer revealed messages critical of Trump's science cuts, "which [says CPB] conveyed hatred of Trump & could be qualified as terrorism". Computer confiscated

I've just turned down an invitation for an event in the US this summer as well. There were multiple reasons, including visa appointment issues, but reading the answers on this thread I think I made the right decision: I would not want to go through ridiculous US customs questioning right now.

Do #exoplanets evolve over time? ☄️ A thread 1/🧵

This Fall we will offer a minor in astronomy at Leiden Observatory! It will be accessible for all non-astronomy Dutch BSc students. This program offers a unique opportunity to explore astronomy’s role in shaping our understanding of the Universe. See studiegids.universiteitleiden.nl/studies/1063...

My BSc students have been digging the ALMA archive and have classified all unresolved low SNR detections as 'disappointing blobs'. 😂

🚨 ESO analysis confirms that the INNA industrial megaproject would have a devastating and irreversible impact on the facilities at Paranal Observatory. Full story ➡️ www.eso.org/public/news/... Details in 🧵 below 👇 🧪 🔭 #astrosci 1/

Are we tired yet of PDS70? It's obviously the topic of many talks at the GAP (Giant Accreting Planets) conference. Nice cartoon by Luna Rampinelli!

One of the employees fired from NASA told me how much their career meant to them: "Prior to everything happening today, NASA has been an incredible place to work — to dream big, to innovate, to do things that I never thought I could have done.” Words by me. 🧪 www.nature.com/articles/d41...

I got one of these again #JWSTCycle4 (credits @astronomay.bsky.social)

Great start of the GAP conference with a "black hole" Zoom image by Kate Follette

Woops! When I googled 'EAS abstract' since the submission deadline is today, I was very surprised to find that I could only submit a "Late breaking abstract" at this date. Turns out I was at the conference website of the European Atherosclerosis Society, instead of European Astronomical Society...

This morning I Googled 'scattered light disk surface' to find an example image. One of the results was a SPHERE image gallery (left), but it immediately changed into a cute kitten (right) due to the 'Make America Kittens Again' filter that changes pictures of Trump to kittens. SPHERE is too orange 😂

I have finally blocked one full afternoon in my weekly calendar for personal science time, and no meetings. I always thought I could do without because of multi-tasking but with increased teaching, supervision and committees I find myself more and more without focus time. Let's see if this works 💪

Fun homework exercise for my students: write an essay about your favorite telescope and why it's your favorite. Some clear popular winners, but also some surprises!

When a postdoc starts introducing himself before a talk as a PhD student, corrects himself and then says "I wish I was still a PhD student". 😂 So relatable! Don't kid yourself, PhD time really is the best time of your career in many ways...

Next week I'm getting out of my comfort zone: talking about galaxies at Astronomy on Tap in Leiden!

Do people remember the Google extension "Make America kittens again"? It replaces all images of Trump on news websites etc. with a picture of a kitten. It is very calming. Again. chromewebstore.google.com/detail/make-...

I was wondering about this too.. 😱

Why is there no such thing as: "I'll download this ALMA dataset quickly and calibrate it with the provided script" when you're on a deadline 😭😭😭

It's paper day! Together with @sijme-jan.bsky.social and led by exceptional (2nd year!) PhD student Jip Matthijsse, we look at the Streaming Instability in dust with size distributions and how the resulting clumps have different size distribution from the initial one arxiv.org/abs/2502.01752 1/n

Happy with the active discussions today at my first lecture! Let's see if it leads to more active engagement this semester. 💪

Why does my Mac continue to autocorrect snowlines to snowiness? 😠

Advice from the exam committee involves a new word: "Think of how ChatGPTable your homework assignments are"

Disgusting 🫣 😭

Ayumu Kuwahara shows yet another way to explain dust gaps in disks: apparently even low-mass Earth-like planets can create them due to the induced gas flow 🤯

Don't we all love a Zoom-Droste-effect-selfie? 😆

Impressed to see there is a new model for astronomy missions: the MAUVE satellite (Blue Skies Space) is built by a private company, and funded by a combination of private investors and grants. Great lunch talk today by Fatemeh Zahra Majidi!

My plan for a group assignment at my first lecture on observing techniques: discuss in groups how to address one of these comments from your 'crazy-uncle-who-does-not-believe-in-science' as an astronomer. Any thoughts? Suggestions?

When you write a publication on a single target (or perhaps a handful), it is worth spending some time on using SIMBAD to find references with a high occurrence score on this target. So much has been published already that it's impossible to keep track, but in this way you still get up to date.

Damn, number of pages is suddenly something to consider now with publishing in A&A!

Me at the end of a group Zoom meeting to my student: "Could you come to my office for a chat after this?" Student: "What have I done? Are you breaking up with me??" Me: 😂😂😂

Today is Gaia's final observing day 😭😭😭

METIS, we are getting started! Within the METIS disk team, we just decided on 7 initial observing programs that will be explored in the coming two months in terms of feasibility, observational settings and target choices. Stuff is getting real!